4/28 Flashcards
(24 cards)
for polar molecules, which modes of vibration are IR active?
all modes of vibrations are IR active because the dipole changes
for nonpolar modes of vibration, which are IR active and inactive?
the symmetric stretches are IR inactive
the asymmetric stretches and bending motions are IR active
for CO2 why do we only see 2 peaks instead of 4?
only 3 of the 4 peaks are IR active, two of the peaks, bending motions are equivalent in energy and overlap at the same peak
what rotational vibrational branch has a lower vibration?
the p branch (J =-1)
what rotational vibrational spectrum branch is larger than the vibrational frequency?
the R branch
what is the missing Q branch?
it is the branch that is missing where delta J = 0
for the vibrational rotational spectrum, what is the separation between two peaks equal to?
it is equal to 2B, which can be used to calculate the rotational constant, bond length and the moment of inertia
whqat does the average between the first P and R peak equal?
it equals the vibrational frequency which can be used to calculate the force constant
what types of light are required for an electronic transition?
UV/Vis
what types of light are required for an Vibrational transition?
Infared light
what types of light are required for a rotational transition?
microwave light
what type of transition requires the highest energy light
electronic transitons (UV)
what type of transition requires the lowest energy light
rotational transitions (microwave light)
for the excited state of a electronic spectrum, how will the bond order and length compare to the bond order of the ground state
the bond order will decrease so the bond length will increase
for an electronic transition, how does the transiiton appear?
it appears as a vertical transition
why does the electronic transition have a vertical transition?
due to the frank condon principle, the nuclei are much heavier than the electrons, meaning that the electrons move much faster and the nuclei appear to be stationary when electrons are excited. This makes it so there is no change in bond length when electrons are excited
according to the frank condon principle, what is the assumption as to why there is a vertical transiton
we assume that the nuclei are stationary when electrons are excited and there is no change in bond length
what determines which peak will be the most intense in the electronic transition spectrum?
the transition where the vertical transition from the ground state intersects
what if the difference in bond lengths between the ground state and excited state is large
the excited state will be shifted to the right on the diagram
the vertical transition will hit a larger nā value and the most intense peak will be shifted to a higher energy
what if the difference in bond lengths between the ground state and excited state is small?
the most intense peak will come at a lower energy and the nā value for the vertical transition is lower
what is a chromophore?
they are functional groups that give characteristic types of electronic transitions
what is a ligan to metal charge transfer
when a transition metal has an empty orbital, a ligand with extra electrons can be excited into this orbital when UV/Vis light is applied
what is a metal to ligand charge transfer
when a transition metal is full, but the ligand has an empty orbital (diatomic molecule), then the electron from the metal can be excited into the ligand
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